what's up it wants to know. Me too. What is a Blue Moon?

Most people nowadays define this as a second Full Moon falling in a calendar month, though this "definition" was invented in the board game Trivial Pursuit in the 1980s.

The others are wrong. Everybody knows it is a particular kind of beer.

It was a very popular song in the 60's.
I think The Platters sang it.

I have heard that it is common to call the second full Moon in a calendar month a "Blue" Moon.
It happens every 13 Lunar months as they don't quite coincide with our calendar.
Last one was in January 2014.
The 1st and the 30th.

A "Blue Moon" is the second full moon in one calendar month.

That's it.

No more. No less.
.

No idea what "what's up it wants to know" - what is "it"?

A blue moon has several definitions.
The most common today is the 2nd full moon in a calendar month.
Other definitions are the 4th full moon in a 3-month timeframe, or the 4th full moon in a season.

Here is the original origin of the term "blue moon",

Origin of the term


The suggestion has been made that the term "blue moon" for "intercalary month" arose by folk etymology, the "blue" replacing the no-longer-understood belewe, 'to betray'. The original meaning would then have been "betrayer moon", referring to a full moon that would "normally" (in non-intercalating years) be the full moon of spring, while in intercalating year, it was "traitorous" in the sense that people would have had to continue fasting for another month in accordance with the season of Lent.[6][7]

The earliest recorded English usage of the term blue moon is found in an anti-clerical pamphlet (attacking the Roman clergy, and cardinal Thomas Wolsey in particular) by two converted Greenwich friars, William Roy and Jerome Barlow, published in 1528 under the title Rede me and be nott wrothe, for I say no thynge but trothe. The relevant passage reads:[8]

O churche men are wyly foxes [...] Yf they say the mone is blewe / We must beleve that it is true / Admittynge their interpretacion. (ed. Arber 1871 p. 114)

It is not clear from the context that this refers to intercalation; the context of the passage is a dialogue between two priest's servants, spoken by the character "Jeffrey" (a brefe dialoge betwene two preste's servauntis, named Watkyn and Ieffraye). The intention may simply be that Jeffrey makes an absurd statement, "the moon is blue", to make the point that priests require laymen to believe in statements even if they are patently false. But in the above interpretation of "betrayer moon", Jeffrey may also be saying that it is up to the priests' to say when Lent will be delayed, by announcing "blue moons" which layman have no means to verify.

A blue moon is an extra full moon that appears in a subdivision of a year, either the third of four full moons in a season or, recently, a second full moon in a month of the common calendar. Metaphorically, a "blue moon" is a rare event, as in the expression "once in a blue moon".

http://en.wikipedia.org/wiki/Blue_moon

If a full moon appears twice in the same month,it's known as Blue Moon. The second full moon that appears on the same monh is called a Blue Moon. It's coming on 31st of July 2015. It's previous full moon is on 2nd of July 2015. In this case the full moon on July 31,2015 is called Blue Moon. No,it's got nothing with appearing blue.

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A blue moon is full moon that occurs as the second full moon in a given month. Blue moons are not typically blue in color — that happens only, well, once in a blue moon

The second full moon in a month with two full moons.

A lunar month averages 29.54 days. The only way you can get a blue moon is if the first day of the month has a full moon, 1/30th of the time for any 30 day month, , or the first or second day of the month for a 31 day month.
There are 7 thirty day months and 4 thirty one day months, so the probability of a blue moon in a given year
is about 1/30 times 7 plus 2/30 times 4, or about 15/30,, so you should get a full moon every couple of years or so.

A blue moon is an extra full moon that appears in a subdivision of a year, either the third of four full moons in a season or, recently, a second full moon in a month of the common calendar.